KR20000070683A - A device in the stator of a rotating electric machine - Google Patents

Abstract

The stator has stator teeth between the slot grooves that receive the windings, the free ends of the teeth having an air cap between the stator and the rotor. A device for increasing the mechanical rigidity and natural frequency of the stator in a rotating electric machine, located in the gap, is formed integrally with adjacent stator teeth. And a yoke disposed across each stator slot groove to mechanically support the stator teeth in a tangential direction.

Description

Stator device for rotating electric machines {A DEVICE IN THE STATOR OF A ROTATING ELECTRIC MACHINE}

The present invention relates to an apparatus for increasing the mechanical rigidity and natural frequency of a stator in a rotating electric machine, the stator supporting a winding. Stator teeth are provided between the slot grooves, and free ends of the teeth are located in the air gap between the stator and the rotor. The invention also relates to such a rotary electric machine.

Generators, dual-fed machines, outer pole machines, synchronous machines and asynchronous static current converter cascades in power plants to generate electric power High-voltage electric alternating current machines, such as converter cascades, have been designed so far with voltages in the range of 15 to 30 kHz, with 30 kHz being generally considered the upper limit. In general, this means that a generator must be connected to the power network through a transformer that raises the voltage to a power network level, ie, in the range of approximately 130 to 400 kW.

U.S. Patent No. 5,036,165 describes one conductor with one semiconducting pyrolized glassfiber and one outer layer with one outer layer formed on the insulation. It is also known to form such insulation in the conductors of a dynamo-electric machine, for example in US Pat. No. 5,066,881 two parallel rods in which a semiconductive pyrolytic glass fiber layer forms the conductors. Insulator in the stator slot groove is surrounded by an outer layer of semiconductive pyrolytic glass fibers. This pyrolytic glass fiber is described as suitable because it still maintains resistivity even after the impregnating treatment.

The solution to this problem is a Swedish patent application which describes a device in which separate spacers, such as slot wedges, are inserted into the space between the free ends of adjacent stator teeth. 9602083-9. One drawback with this solution is that the slot wedges are easily loosened by the difference in the stator teeth and the thermal expansion of the stator teeth and slot wedges.

A special system of slot wedges adapted to be inserted into a stator slot groove is also disclosed in US Pat. No. 4,443,725. However, the purpose of this wedge system is not to increase the rigidity of the stator teeth, but to support the electrical conductors in the correct position in the stator slot grooves.

It is an object of the present invention to provide a new solution, in the form of alternating current machines discussed below, against the problem of vibrations occurring in the stator teeth, without the disadvantages of the previous method.

This object is achieved by an apparatus of the type described in the introductory part of the present invention and a machine described in claim 10 having the features defined in claim 1.

By installing at least one rigidity-increasing yoke in one piece across each stator slot groove with adjacent stator teeth, the yoke supporting the stator teeth is in a tangential direction. The risk of loosening is eliminated.

According to a preferred embodiment of the device according to the invention, a yoke is formed at the top of the slot. This yoke position allows the yoke to serve as an optimal mechanical bracing for the stator teeth.

According to another preferred embodiment of the device according to the invention, the yoke may be formed across the slot groove at a certain distance from the top of the slot groove, whereas a plurality of yokes may have different distances from the top of the slot groove. It may be formed across the slot groove.

According to another preferred embodiment of the present invention, the width of the yoke in the tangential direction of the slot groove should be generally at least 2-3 mm so that the yoke can absorb the loads which increase in the tangential direction. Closing the slot grooves of the stator in this way negatively affects the electrical properties of the machine, causing the yoke or yokes to increase slot groove leakage, resulting in the need for excitation of the load, i.e. field windings. This can lead to increased losses in windings. The increase in slot leakage also affects the transient reactance of the machine.

Closing the slot grooves also results in slot groove harmonics in the air gap flux such that only a fraction of 5-15% of the harmonics obtained by the open slots remains. slot harmonic) Therefore, all the noise generated by the slot groove harmonics is largely eliminated.

In order to reduce the increase in the above mentioned excitation losses due to the closed stator slot grooves, the yoke according to a preferred embodiment of the device according to the present invention has a deviation of the magnetic properties of the yoke from the magnetic properties of the stator teeth. It should be made as deviation as possible. Thus, the yoke is processed by, for example, perforated yoke or by processing the yoke material, for example laser-, in order to lower its relative magnetic permeability, preferably to a value close to one. worked, the relative permeability in the yoke material can be such that the structure is close to one.

The present invention is primarily designed for use with a rotary electric machine, wherein the stator windings are wound through slot grooves in the stator, the windings being one core having a plurality of wires, one interior surrounding the core A high voltage cable having a shape including a semiconducting layer, one insulating layer surrounding the inner semiconducting layer, and one outer semiconducting layer surrounding the insulating layer is wound. Called high voltage cables below, the use of high voltage insulated electrical conductors with solid insulation similar to that used for cables for power transmission (e.g. XLPE cables) allows the machine to power the network without a single intermediate transformer. The voltage of the machine can be increased to such a level that can be connected directly. Thus, the transformer can be omitted. In this type of machine, the slot grooves in which the cables are located in the stator are generally deeper than in the prior art, because thicker insulation is due to higher voltages and more turns in the windings. Because it is required. This increases the problems of mechanical natural vibrations of the stator teeth between the stator slot grooves. In a stator with deep slot grooves, damaging vibrations easily occur, which are caused by electromagnetic forces and resonance phenomena, and generally have twice the frequency of the network frequency. Thus, the device according to the invention is particularly advantageous for machines of this kind.

In the machine according to the invention, the windings preferably consist of a cable of the type with a solid extrusion insulation, which is currently used for distribution, for example an XLPE cable or a cable with an EPR insulation. . Such a cable comprises one inner conductor having at least one element, one inner semiconducting layer surrounding the conductor, one solid insulating layer surrounding the semiconducting layer and one outer semiconducting layer surrounding the insulating layer. . Such a cable is flexible and the technique of the device according to the invention is based on a winding system which is inherently formed of conductors which are bent at assembly, so flexibility is an essential property in this regard. Flexibility of XLPE-cables typically corresponds to a radius of curvature of approximately 20 cm for cables with a diameter of 30 mm and a radius of curvature of approximately 65 cm for cables with a diameter of 80 mm. In the present application, the term "flexibility" is used to indicate that the winding has a radius of curvature of about four times the cable diameter, preferably about eight to twelve times the cable diameter.

It is preferred that the cable has a diameter in the range of 20 to 200 mm and a conductive area in the range of 80 to 3000 mm 2.

The windings are configured to retain their properties when they are bent and even when under thermal stress during operation. In this relationship, it is very important for the layers to maintain adhesion to each other. Here, the material properties of the layers, in particular the elasticity and relative coefficients of thermal expansion, are crucial. In XLPE-cables, for example, the insulating layer consists of cross-linked low density polyethylene, and the semiconducting layer consists of polyethylene with mixed soot and metal particles. The change in volume with temperature changes is fully absorbed as the radius of the cable changes, and since the difference in coefficients of thermal expansion in the layers relative to the stretch of these materials is relatively small, radial expansion can occur without loss of adhesion between the layers. have.

It should be appreciated that the combination of materials described above is merely an example. The above-mentioned conditions and conditions that become semiconducting, that is, conditions having a resistivity within the range of 10 ⁻¹ to 10 ⁶ ohm-cm, for example, 1 to 500 ohm-cm or 10 to 200 ohm-cm Other combinations that meet the conditions are, of course, included in the scope of the present invention.

The insulating layer is, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polybutylene (PB), polymethylpentene (PMP), crosslinked polyethylene (XLPE) and ethylene It may be made of a solid thermoplastic such as rubber such as propylene rubber (EPR) or silicone rubber.

The inner and outer semiconducting layers may be made of the same base material, but may include particles of a conductive material such as mixed leaded or metal powder.

The mechanical properties of these materials, in particular the coefficients of thermal expansion, are relatively unaffected, at least within the proportions necessary to achieve the conductivity requirements according to the invention, whether or not the cast or metal powder is mixed. Thus, the insulating layer and the semiconducting layers generally have the same coefficient of thermal expansion.

Ethylene-vinyl-acetate copolymer / nitrile rubber (EVA / NBR), butyl graft polyethylene, ethylene-butyl-acrylate-copolymer (EBA) and ethylene-ethyl-acrylate copolymer (EEA) It also belongs to a polymer suitable as a semiconducting layer.

Although other types of materials are used as the base in the various layers, it is preferable that the coefficients of thermal expansion of the materials are generally the same. This is the case when the substances listed above are combined.

The materials listed above have a relatively good elasticity with an E-modulus of E <500 MPa, preferably of <200 MPa. The elasticity is sufficient to be absorbed by the elasticity in the radial direction even if there is a small difference between the coefficients of thermal expansion of the materials in the layers, so that no cracks or other damages occur and the layers do not separate from each other. The material in the layers is elastic and the adhesion between the layers is at least at the same level as the weakest of the materials.

The conductivity of the two semiconducting layers is sufficient to make the potential difference of each layer substantially uniform. The conductivity of the outer semiconducting layer is large enough to enclose the electric field in the cable, but small enough to not cause significant losses due to the current induced in the longitudinal direction of the layer.

Thus, the two semiconducting layers each essentially constitute one equipotential surface, with the windings having these layers generally surrounding the electric field therein.

Of course, nothing prevents one or more additional semiconducting layers from being placed in the insulating layer.

The present invention will be described below with reference to the accompanying drawings.

In the accompanying drawings, FIG. 1 is a partial view of one slot groove of a stator having an open slot, FIG. 2 is a partial view of one slot groove designed by the present invention, and FIG. 4 is a diagram showing a cross section of a high voltage cable used by the present invention.

FIG. 1 shows a partial view of one slot groove of a sheet iron core in a stator, in which one slot groove 2 and stator teeth 4 on each side of the slot groove 2 are shown. , 6). The slot groove 2 is configured to receive a winding cable 12 extending axially through the stator, which slot grooves 2 are usually deeper in the case of an AC machine of this type than a conventional machine. . This, as mentioned above, leads to drawbacks due to vibrations that easily occur in stators and stator teeth 4, 6 having a low natural frequency.

As shown in FIG. 1, the slot grooves 2 of this type of machine, unlike conventional generators, are located between each cable 12 in the teeth 4, 6 located between the slot grooves 2. Since it is shaped like a bicycle chain with formed projections 10, the cable is fixed radially. Thus, in order to distinguish it from conventional open, rectangular slots having sides that are completely straight towards the air gap, this type of slot groove is often referred to as "semi-closed". Known.

The slot groove 2 is open to the air gap at the slot top, ie to the left in FIG. 1. The opposite end of the slot groove is called the slot bottom.

In order to solve the problem of natural vibration in the stator described above and to increase tangential rigidity, a yoke 14 is formed across the slot grooves by the present invention (see FIG. 2). In the embodiment shown in this figure, one yoke is arranged above the slot groove and the other yoke is arranged almost in the center of the slot groove 2. If you select the most effective yoke position from a mechanical point of view, it is the top of the slot groove. However, when the slot groove is deep, it may be a good idea to install several yokes, in some cases it is not desirable to place the yoke on top of the slot groove, and it may be desirable to install the yoke only at the innermost point. . Yoke (or yoke) 14 is made in one piece with adjacent stator teeth 4, 6. By achieving tangential stability by the yokes 14, the natural frequency is increased, not only increasing flexural rigidity over the entire stator body, but also significantly increasing the rigidity of each individual tooth. Another important advantage is that the tangential electromagnetic force in the air gap coming out of the rotor poles is evenly distributed between the teeth.

In order for the yoke or the yokes 14 to provide sufficient mechanical bracing, the width d of the yoke in the slot groove 2 direction should generally be at least 2-3 mm.

As mentioned above, the yokes increase slot leakage. In the case of short-circuiting, an increase in leakage flow limits short-circuit currents and eliminates or at least reduces slot harmonics of the air gap flux. However, increased slot groove leakage increases excitation losses. For this reason, the yoke or yokes 14 are preferably made so that their magnetic properties deviate from the magnetic properties of the stator teeth 4, 6. The yoke is preferably configured such that the relative magnetic permeability of the yoke material is close to one. This can be accomplished by puncturing the yoke, as shown at 16 in FIG. 3. In that case, however, it must be ensured that the holes do not prevent the yoke or the stabilization action of the yokes. Alternatively, the permeability of the yoke material can be reduced by proper treatment of the material, for example laser treatment.

4 shows a cross-sectional view of a high voltage cable 29 used in a rotary electric machine according to the present invention.

The high voltage cable 29 comprises a plurality of element sections 31, for example made of copper and having a circular cross section. The element wires 31 are disposed at the center of the high voltage cable 29, and the first semiconducting layer 32 is around the element wires 31. In the circumference of the first semiconducting layer 32, there is an insulating layer 33, which is, for example, an XLPE insulator, and there is a second semiconducting layer 34 around the insulating layer 33.

Claims (18)

The stator has a stator tooth between the slot grooves supporting the windings, the free end of the tooth being located in the air gap between the stator and the rotor. In an apparatus for increasing the mechanical rigidity and natural frequency of a stator, at least one yoke designed to increase the stiffness and formed integrally with an adjacent stator tooth is provided with a stator tooth. Stator device of a rotary electric machine, characterized in that it is disposed across each stator slot groove for mechanical support in a tangential direction. 2. The stator device of a rotary electric machine according to claim 1, wherein the yoke is formed on an upper portion of the slot groove. The stator device of claim 1, wherein the yoke is formed to traverse the slot groove at a predetermined distance from an upper portion of the slot groove. The stator device of a rotary electric machine according to claim 1, wherein the width of the yoke in the slot groove direction is more than a lower limit of typically 2 to 3 mm. The stator device of claim 1, wherein a plurality of yokes are formed across the slot grooves at different distances from the top of the slot grooves. The rotary electric machine according to claim 1, 2, 3, 4 or 5, wherein the yoke is configured such that its magnetic properties are shifted from the magnetic properties of the stator teeth. Stator device of the machine. The stator device of claim 6, wherein the yoke is configured such that the relative magnetic permeability of the yoke material is close to one. 8. The stator device of a rotary electric machine according to claim 6 or 7, wherein the yoke is perforated. The stator device of a rotary electric machine according to claim 6, 7, or 8, wherein the material of the yoke is processed to lower permeability. 10. A rotating electric machine having windings received in a slot groove of a stator, said windings being wound with a high voltage cable and having the device as claimed in any one of claims 1 to 9. The method of claim 10, wherein the high-voltage cable is one core having a plurality of wires 31, one inner semiconducting layer surrounding the core, one insulating layer surrounding the inner semiconducting layer and the insulating layer A rotary electric machine, characterized in that it comprises a single outer semiconducting layer surrounding. 12. The rotary electric machine according to claim 11, wherein the high voltage cable has a diameter in the range of 20 to 200 mm and a conductive area in the range of 80 to 3000 mm2. 13. A rotary electric machine according to claim 10, 11 or 12, characterized in that the winding is flexible and the layers are sticking together. The method according to claim 10, 11 or 12, wherein the change in volume in the layers according to the change in temperature during operation is completely absorbed by the elasticity of the material, so that the mutual adhesion to the change in temperature occurring during operation And the layers are made of a material having a relationship between such elasticity and the coefficient of thermal expansion of the material. 8. A rotary electric machine according to claim 6 or 7, characterized in that the material of the layers has a high elasticity, preferably an elastic modulus of 500 MPa or less, more preferably an elastic modulus of 200 MPa or less. 16. A rotary electric machine according to claim 10, 11, 12, 13, 14 or 15, characterized in that the coefficient of thermal expansion of the material of the layers is about the same. The method according to claim 10, 11, 12, 13, 14, 15 or 16, characterized in that the adhesion between the layers is at least about the same as the weakest material, Rotary electric machine. The method according to claim 10, 11, 12, 13, 14, 15, 16, or 17, wherein each semiconducting layer essentially constitutes one equipotential surface. Made, rolling electric machine.